Surgical tourniquet systems are commonly used to stop the flow of arterial blood into a portion of a patient's limb, thus creating a clear, dry surgical field that facilitates the performance of a surgical procedure and improves outcomes. A typical surgical tourniquet system of the prior art includes a tourniquet cuff for encircling a patient's limb at a desired location, a tourniquet instrument, and flexible pneumatic tubing connecting the cuff to the instrument. In some surgical tourniquet systems of the prior art, the tourniquet cuff includes an inflatable portion, and the inflatable portion of the cuff is connected pneumatically through flexible plastic tubing and one or more connectors to a tourniquet instrument. A typical tourniquet instrument of the prior art includes a pressure regulator to maintain the pressure in the inflatable portion of the cuff, when applied to a patient's limb at a desired location, near a reference pressure that is above a minimum pressure required to stop arterial blood flow past the cuff during a time period suitably long for the performance of a surgical procedure. Many types of such pneumatic surgical tourniquet systems have been described in the prior art, such as those described by McEwen in U.S. Pat. No. 4,469,099, No. 4,479,494, No. 5,439,477 and by McEwen and Jameson in U.S. Pat. No. 5,556,415 and No. 5,855,589.
In surgical tourniquet systems of the prior art, leakage of pressurized gas from the tourniquet cuff, or from pneumatic tubing between the instrument and cuff, or from connectors attaching the tubing to the cuff and instrument may affect safety, performance, and reliability. The 2007 Recommended Practices for the Use of the Pneumatic Tourniquet in the Perioperative Practice Setting (RPs) of the US Association of periOperative Nurses (AORN) recommend that the tourniquet cuff, tubing, and connectors should be kept clean and in good working order. The AORN RPs further recommend, based on published literature, that the tourniquet cuff, tubing, and connectors should be inspected for cracks and leaks because unintentional pressure loss can result from loose tubing connectors, deteriorated tubing, or cuff bladder leaks, and may result in patient injury. At present, such inspections and checking are performed manually and often inconsistently by users, or only after a hazardous incident or patient injury has occurred. As a result, defective and leaking tourniquet cuffs, connectors and tubing may remain in use for long periods of time. Also, users may not be alerted to defects which may be small initially but which may increase to become significant hazards, either slowly or very rapidly, if remedial action is not taken. Unauthorized reprocessing and reuse of cuffs manufactured to be single-use disposable cuffs may introduce leakage hazards if such cuffs are not carefully inspected and checked before each reuse because improper, uncontrolled and unlimited reprocessing may impair the shape and integrity of the pneumatic seals of cuff connectors. Even if disposable tourniquet cuffs are used as single-use products, and if it is assumed that such cuffs are not leaking at time of first use, the tubing and connectors that connect the disposable cuffs to the tourniquet instrument may leak and such leakage may go undetected, allowing the leaking tubing or connectors to remain in use until an obvious patient hazard or injury occurs, and during which time other limitations in tourniquet safety, performance and reliability are produced, as described below.
To alert a user to an extreme loss of tourniquet cuff pressure from leakage, for example as may be caused by a pneumatic disconnection between the cuff and the instrument, some surgical tourniquet systems of the prior art include audio-visual leakage alarms. Unfortunately, such alarms in prior-art systems are typically produced only after there has been a decrease in actual cuff pressure to a level that is well below the reference pressure for a sustained period of time, and thus only after substantial blood flow past the cuff may have occurred. This adversely affects the safety and quality of surgery before the user is alerted to the need for remedial action.
Sustained pneumatic leakage that is not detected by prior-art tourniquet systems is undesirable in surgery and may be hazardous. In the past, undetected pneumatic leakage led users of prior-art systems to set tourniquet pressures at reference levels that were substantially higher than required physiologically to compensate for intra-operative reductions in cuff pressure that users had observed but had not been able to attribute to obvious leakage. However, setting unnecessarily high pressures is hazardous because in the medical literature higher tourniquet pressure levels have been associated with higher probabilities of patient injuries to nerves and soft tissues. More recently, some surgical tourniquet systems of the prior art have attempted to compensate for undetected levels of pneumatic leakage in the design of their pressure regulators. In typical systems, the pressure regulator is designed to maintain cuff pressure within a predetermined pressure range from a reference pressure, and any fluctuations beyond that range are offset by actuation of a pump, reservoir, or valve in an effort to bring the cuff pressure back within the range. If there is pneumatic leakage sufficient to cause the cuff pressure to decrease beyond the predetermined pressure range, actuation of the pressure regulator may bring it back within range, and if not a pressure-regulation alarm is produced. Such systems of the prior art may compensate for significant levels of sustained, undetected leakage without producing any indication of leakage or alarm for the user. As a result of this limitation, defective and leaking tourniquet cuffs, connectors, and tubing may remain in use for long periods of time. Further, sustained leakage may produce an error in the indicated tourniquet cuff pressure in single-port tourniquet systems of the prior-art which estimate cuff pressure by measuring pneumatic pressure within the tourniquet instrument. Also, users are not alerted to defects which may be small initially but which may increase to become significant hazards, either slowly or very rapidly, if remedial action is not taken. For typical surgical tourniquet systems of the prior art three limitations in the performance and reliability of their pressure regulators exist in the presence of undetected pneumatic leakage. First, tourniquet cuff pressure fluctuates unnecessarily as decreases in cuff pressure are offset by the actuations of the pressure regulator. Second, unnecessarily frequent actuation of the pressure regulator reduces the operational life and reliability of its mechanical components, increases the cost of maintaining and replacing those components, and may increase capital costs by necessitating early replacement of the entire tourniquet instrument. Third, operation of prior-art tourniquet systems on battery power is impaired. Typical tourniquet systems of the prior art may be powered either by external AC power or by an internal battery, so that they can continue to operate safely in the event of a sudden interruption of external power, and so that they can operate independently of external AC power for a prolonged period of time, for example during transportation of a patient from a pre-operative room to the operating room, or to facilitate surgery under emergency or battlefield conditions. However, in the presence of sustained leakage pneumatic leakage, the operational time of a tourniquet system when powered by an internal battery for surgery may be substantially reduced due to unnecessary actuations of the pressure regulator. Additionally, the overall life of the internal battery may be significantly reduced, reducing the performance and reliability of the tourniquet system and thereby increasing costs and hazards.
There is a need for a leak detector for surgical tourniquet systems that overcomes the above-described limitations of the prior art. No surgical tourniquet system known in the prior art rapidly detects leakage in the tourniquet cuff, pneumatic tubing, or pneumatic connectors between the cuff and pressure regulator of the tourniquet instrument while cuff pressure is maintained near a reference pressure by the pressure regulator. Further, no system known in the prior art estimates the magnitude of pneumatic leakage while cuff pressure is regulated near the reference pressure. No prior-art system determines the level of hazard to a patient associated with the magnitude of any pneumatic leakage estimated during cuff pressure regulation. Also, no prior-art tourniquet system includes means for communicating with a remote display, printer, alarm or similar apparatus to produce an indication perceptible by a user of the level of hazard associated with any pneumatic leakage detected during cuff pressure regulation.